Bimetallic Cobalt Based Catalysts

Highly dispersed, oxide- or zeolite-supported bimetallic catalysts are widely used in the catalytic industry, such as in catalytic reforming, nitrogen industry and gas-to-liquid technology. The paper highlights the nano-sized Co-based bimetallic system in terms of correlation between structure and reactivity/selectivity promoted by the second metal. Opposite to the bulk alloys nano-sized bimetallic catalysts are extremely sensitive to the structure, morphology, valence state of the supporting oxide material in which the nano-particles are embedded. In this case, one of the less reducible components, which strongly interact with the supports, may stabilize the second, more noble metals, and thus the latter can be stabilized in highly dispersed state. Conversely, addition of noble metal to the hardly reducible component may facilitate reduction, which causes the retardation of the deactivation process of some hydrocarbon reaction. The future trend is the application of bimetallic nano-particles although careful consideration and experimentation should be taken to elucidate the structure of such type of catalyst. The various effects of Co-based bimetallic particles, such as particle size, metal/support interface, morphology and electronic effects, on the activity/selectivity in given catalytic reactions will be discussed.     

New opportunities to understand heterogeneous catalysis processes on nanoscale bimetallic particles through synchrotron radiation and theoretical studies

New advances in theoretical background and recent experimental results concerning nanoscale bimetallic clusters are presented. From theoretical point of view, we will show how both the relaxation of the intermetallic distances and the chemical local ordering can be predicted from the electronic structure. Here, we compare these predictions at thermodynamical equilibrium to a review of recent results obtained using XAS for bimetallic systems Pt–M where M is a 4d transition metal. Even though the distribution of the two species inside the cluster can be affected by preparation parameters, such as, the nature of the precursor, it appears that these theoretical calculations are a valuable starting point for the study of such entities.     

Degradation of ultrahigh concentration pollutant by Fe/Cu bimetallic system at high operating temperature

To investigate the degradation of high concentration pollutant by Fe/Cu bimetallic system at a high operating temperature, 10,000mg/L acid orange 7 (AO7) aqueous solution was treated by Fe/Cu bimetallic system at 80 oC. First, the effect of the operating temperature (30-80 °C) on the reactivity of Fe/Cu bimetallic particles was investigated thoroughly. Then, the studies on the effect of theoretical Cu mass loading, Fe/Cu dosage, stirring speed and initial pH on the reactivity of Fe/Cu bimetallic particles at a high temperature (i.e., 80 °C) were carried out, respectively. The degradation and transformation process of AO7 was studied by using COD, TOC and UV-Vis spectra. The results indicate that high concentration pollutant could be removed effectively by Fe/Cu bimetallic system at a high operating temperature. And the removal efficiencies of AO7 by Fe/Cu bimetallic system were in accordance with the pseudofirst- order model. Finally, it was observed that the high temperature could accelerate mass transport rate and overcome the high activation energy barrier to significantly improve the reactivity of Fe/Cu bimetallic particles. Therefore, the higher removal efficiency could be obtained by Fe/Cu system at a high operating temperature. Thus, the high operating temperature played a leading role in the degradation of high concentration pollutant.     

Chemisorption Complexes on Alloy Surfaces

Three factors have greatly promoted the recent revival of interest in catalysis by alloys.

The first was the finding that in industrial catalysis certain bimetallic systems are superior to monometallic catalysts. Sinfelt [1-5] had a particularly important share in the pioneering work supporting this finding. He showed that the selectivity for catalyzing nondestructive hydrocarbon reactions is often significantly tighter for a bimetallic catalyst than for its most active monometallic constituent. Even more important was the finding that bimetallic catalysts are frequently less susceptible to poisoning by, e.g., carbonaceous residues [1-6], As a consequence, their steady-state activity will be superior to that of monometallic catalysts even if the initial activity was lower.     

Chemisorption Complexes on Alloy Surfaces

Abstract

Three factors have greatly promoted the recent revival of interest in catalysis by alloys.

The first was the finding that in industrial catalysis certain bimetallic systems are superior to monometallic catalysts. Sinfelt [1–5] had a particularly important share in the pioneering work supporting this finding. He showed that the selectivity for catalyzing nondestructive hydrocarbon reactions is often significantly tighter for a bimetallic catalyst than for its most active monometallic constituent. Even more important was the finding that bimetallic catalysts are frequently less susceptible to poisoning by, e.g., carbonaceous residues [1–6], As a consequence, their steady-state activity will be superior to that of monometallic catalysts even if the initial activity was lower.     

负载型纳米零价铁及含铁双金属颗粒降解氯代有机物的研究进展

零价铁及含铁双金属颗粒因对氯代有机物降解效率高,而受到国内外的广泛关注.目前该领域的研究热点是纳米铁的改性研究.主要对零价铁及含铁双金属颗粒的负载改性、降解氯代有机物过程中主要的影响因素作了介绍.对颗粒负载改性技术存在的问题作了简要的探讨,并且展望了该技术的应用前景和发展趋势.     

Behaviour of Ag,Cu and Ag-Cu catalysts in the gasification reaction of a lignite char in air. Effect of SO2 on these catalysts

The effect of several Ag, Cu and bimetallic Ag-Cu catalysts have been studied on the gasification reaction of a lignite char in dry air. In the bimetallic catalysts, the existence of alloy particles have been detected by SEM. The reactivity of the char with the bimetallic catalysts is higher than the addition of those obtained for the pure metals with the same metal amounts. The effect of SO₂ is to reduce the reactivity of the char in the catalysed reactions. An explanation for this phenomenon is given. The presence of Cu in Ag increases the resistance of some bimetallic catalysts to poisoning with SO₂.     

Near Surface Phase Transition of Solute Derived Pt Monolayers

As the loadings of precious metals in surface-chemical systems continue to decrease for photo-and electro-catalysts for energy and environmental applications, the study of near-surface electronic and atomic structure in functional materials becomes critically important. Extremely small quantities of active elements, whether grown as clusters or ultrathin films, exhibit changes in catalytic activity that arise from both size effects and electron-transfer effects. These size and transfer effects can be related to increased propensity for oxidation of the metallic deposit, as well as to various changes in electrochemical performance such as durability or required overpotential for a given reaction. This work establishes a minimum threshold for Pt loading beyond which bulk-type electronic behavior may be expected. By iteratively growing atomic monolayers and multilayers using self-limited electrodeposition and studying these films using core-electron spectroscopy (X-ray absorption and X-ray photoelectron spectroscopy), electrochemical methods and DFT-based computations the fundamental interactions that govern oxidation state and electron transfer near the surface of a Pt–Au bimetallic system have been explored. It has been shown that the Pt–Au system exhibits increased tendency for the Pt layer to remain cationic below a minimum threshold film thickness of two monolayers. At monodispersed levels of submonolayer coverage Pt exhibits deviated electronic structure, reactivity, and metal stability compared to films in excess of this minimum threshold thickness. At three monolayers Pt is thick enough to avoid the preference for cationicity and the resulting higher rates of metal dissolution, but thin enough to benefit from electron transfers from Au that assist in lowering the overpotentials for CO oxidation. This study shows the efficacy of a concerted method for the investigation of near-surface phenomena in multicomponent systems. By combining electrochemical and vacuum studies of solute-derived samples with advanced computational techniques, a multifaceted understanding of these architectures has been achieved.     

Dopant-induced 2D-3D transition in small Au-containing clusters: DFT-global optimisation of 8-atom Au-Ag nanoalloys

A genetic algorithm (GA) coupled with density functional theory (DFT) calculations is used to perform global optimisations for all compositions of 8-atom Au-Ag bimetallic clusters. The performance of this novel GA-DFT approach for bimetallic nanoparticles is tested for structures reported in the literature. New global minimum structures for various compositions are predicted and the 2D-3D transition is located. Results are explained with the aid of an analysis of the electronic density of states. The chemical ordering of the predicted lowest energy isomers are explained via a detailed analysis of the charge separation and mixing energies of the bimetallic clusters. Finally, dielectric properties are computed and the composition and dimensionality dependence of the electronic polarizability and dipole moment is discussed, enabling predictions to be made for future electric beam deflection experiments.     

Observation of anomalous reactivities of Ni/Pt(111) bimetallic surfaces

We have investigated the surface reactivities of Ni/Pt(111) bimetallic model catalysts using ethylene and cyclohexene as probing molecules. The bimetallic surfaces were generated by evaporating Ni onto a Pt(111) single- crystal surface held at 600 K. The surface chemistry was investigated using high-resolution electron energy loss spectroscopy (HREELS), Auger electron spectroscopy (AES), temperature-programmed desorption (TPD) and low-energy electron diffraction (LEED). The reactivities of the bimetallic surfaces were compared with those of the clean Pt(111) surface and a thick Ni(111) film on the Pt(111) substrate. Formation of the bimetallic surface led to a significantly reduced reactivity towards the decomposition of ethylene when compared to either Pt(111) or Ni(111)/Pt(111) surfaces. Furthermore, although the surface reactivity towards cyclohexene was retained for the bimetallic surface, the decomposition mechanism was distinctly altered from that of either Pt(111) or Ni(111)/Pt(111) surfaces. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structure of Pt–Co/Al2O3 and Pt–Co/NaY Bimetallic Catalysts: Characterization by In Situ EXAFS,TPR, XPS and by Activity in Co (Carbon Monoxide) Hydrogenation

Temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and in situ extended X-ray absorption fine structure (EXAFS) studies were performed to investigate Pt-Co/NaY and Pt-Co/Al₂O₃ bimetallic catalysts. The EXAFS experiments were carried out at the Pt L_III and Co K edges of the same sample. This particular approach allows a precise determination of the electronic and structural characteristics of the metallic part of the catalyst. For both systems in situ reduction under pure H₂ results in the formation of nanometer-scale metallic clusters. For both Co and Pt, nearest neighbors are Co atoms. The complete set of parameters implies the presence of two families of nanometer-scale metallic clusters: monometallic Co nanosized particles and Pt-Co bimetallic clusters, in which only Pt-Co bonds exist (no Pt-Pt bonds). TPR and XPS results indicating a reduction of Co²⁺ ions in Pt-Co/NaY to a greater extent than in Pt-Co/Al₂O₃ give evidence of a facilitated reduction. XRD also shows the presence of nanometer-scale particles with only a very small fraction of larger bimetallic particles. In subsequent mild oxidation of the reduced systems the Co nanoparticles are still present inside the supercage of NaY zeolite in bimetallic form and the oxidation of the metallic particles is slowed down. Catalytic behavior is in good agreement with the structure of the Pt-Co bimetallic system.     

Nanocrystal and surface alloy properties of bimetallic Gold-Platinum nanoparticles

We report on the correlation between the nanocrystal and surface alloy properties with the bimetallic composition of gold-platinum(AuPt) nanoparticles. The fundamental understanding of whether the AuPt nanocrystal core is alloyed or phase-segregated and how the surface binding properties are correlated with the nanoscale bimetallic properties is important not only for the exploitation of catalytic activity of the nanoscale bimetallic catalysts, but also to the general exploration of the surface or interfacial reactivities of bimetallic or multimetallic nanoparticles. The AuPt nanoparticles are shown to exhibit not only single-phase alloy character in the nanocrystal, but also bimetallic alloy property on the surface. The nanocrystal and surface alloy properties are directly correlated with the bimetallic composition. The FTIR probing of CO adsorption on the bimetallic nanoparticles supported on silica reveals that the surface binding sites are dependent on the bimetallic composition. The analysis of this dependence further led to the conclusion that the relative Au-atop and Pt-atop sites for the linear CO adsorption on the nanoparticle surface are not only correlated with the bimetallic composition, but also with the electronic effect as a result of the d-band shift of Pt in the bimetallic nanocrystals, which is the first demonstration of the nanoscale core-surface property correlation for the bimetallic nanoparticles over a wide range of bimetallic composition. Electronic Supplementary Material  Supplementary material is available to authorised users in the online version of this article at     

氢氧直接合成过氧化氢催化剂研究进展

从性组分和载体两方面,总结了近年来氢氧直接合成过氧化氢催化剂的研究进展,重点介绍了Au-Pd、Pt-Pd双金属催化剂在氢氧直接合成过氧化氢中的应用研究。指出负载型纳米双金属催化剂将是氢氧直接合成过氧化氢催化剂研究的发展方向。摘要：从活性组分和载体两方面，总结了近年来氢氧直接合成过氧化氢催化剂的研究进展，重点介绍了Au—Pd、Pt—Pd双金属催化剂在氢氧直接合成过氧化氢中的应用研究。指出负载型纳米双金属催化剂将是氢氧直接合成过氧化氢催化剂研究的发展方向。     

On-Board Hydrogen Production Through Catalytic Exhaust-Gas Reforming of Isooctane: Efficiency of Mixed Oxide Catalysts Ce2Zr1.5Me0.5O8 (Me = Co, Rh, or Co–Noble Metal)

Isooctane reforming under conditions which are set by exhaust gas can be built on to generate hydrogen on-board. Isooctane reforming reactivity tests have been performed with bimetallic catalysts Co–Noble Metal/ceria–zirconia. Variable activity of noble metals doped catalysts, depending on the nature of the noble metal, its loading, and affected by the activation process, is discussed.     

Treatment of chlorinated organic contaminants with nanoscale bimetallic particles

Nanoscale bimetallic particles (Pd/Fe, Pd/Zn, Pt/Fe, Ni/Fe) have been synthesized in the laboratory for treatment of chlorinated organic pollutants. Specific surface areas of the nanoscale particles are tens of times larger than those of commercially available microscale metal particles. Rapid and complete dechlorination of several chlorinated organic solvents and chlorinated aromatic compounds was achieved by using the nanoscale bimetallic particles. Evidence observed suggests that within the bimetallic complex, one metal (Fe, Zn) serves primarily as electron donor while the other as catalyst (Pd, Pt). Surface-area-normalized reactivity constants are about 100 times higher than those of microscale iron particles. Production of chlorinated byproducts, frequently reported in studies with iron particles, is notably reduced due to the presence of catalyst. The nano-particle technology offers great opportunities for both fundamental research and technological applications in environmental engineering and science.     

Dimerization reactions with iron and cobalt bis(imino)pyridine catalysts: A substrate based approach

Herein, we present a substrate based approach to gain insight into effects on reactivity as well as selectivity of dimerization reactions using bis(imino)pyridine catalysts. Common iron and cobalt systems show several limitations applying sterically demanding alkenes. Systematic substrate alterations reveal that structural properties are able to influence reactivity and dimer selectivity whereas electronic properties have an impact on insertion selectivity. Finally, successful conversion of the simplest vinylidene compound isobutene is achieved by catalyst variation.     

Pt/Co和Pt/Ni双金属纳米溶胶制备及催化制氢

采用化学共还原法制备聚乙烯吡咯烷酮(PVP)稳定的Pt/Co和Pt/Ni双金属纳米溶胶,采用UV-Vis、TEM等对所合成的Pt/Co和Pt/Ni双金属纳米溶胶进行表征,研究了化学组成对双金属纳米溶胶催化剂催化NaBH4水解制氢的影响. 结果表明,所制双金属纳米溶胶的平均粒径约为2.0 nm,双金属纳米溶胶的催化能力高于单金属Pt, Co, Ni纳米溶胶,Pt/Co和Pt/Ni双金属纳米颗粒优异的催化性能可归因于电荷转移效应,Co或者Ni原子与Pt原子之间发生的电荷转移效应使得Pt原子带负电而Co或者Ni原子带正电,荷电的Pt和Co、Ni原子成为催化反应的活性中心,促进了催化反应的进行.     

Synergistic activity of gold-platinum alloy nanoparticle catalysts

The understanding of the composition–activity relationship is essential for the exploitation of the synergistic properties of multimetallic nanoparticles in catalytic reactions. This paper focuses on the discussion of findings from the investigation of bimetallic gold-platinum (AuPt) nanoparticles of different compositions. Infrared spectroscopic data for CO adsorption on silica-supported AuPt nanoparticles reveal that the surface binding sites are dependent on the bimetallic composition. The analysis of this dependence further led to the conclusion that the relative Au-atop and Pt-atop sites for the linear CO adsorption on the nanoparticle surface are not only correlated with the bimetallic composition, but also with the electronic effect as a result of the d-band shift of Pt in the bimetallic nanocrystals, which is the first demonstration of the nanoscale core–surface property correlation for the bimetallic nanoparticles over a wide range of bimetallic composition. A further examination of the electrocatalysis data for methanol oxidation reaction on carbon-supported AuPt nanoparticle catalysts reveal important insights into the participation of CO or OH adsorption on Au sites and the catalytic activity of Pt in the AuPt alloys with relatively high Au concentration. Implications of these findings to synergistic correlation of the bifunctional activity of the bimetallic nanoparticle catalysts with the bimetallic composition are also discussed.     

The potential of N-heterocyclic carbene complexes as components for electronically active materials

The application of N-heterocyclic carbene complexes as active sites in materials other than catalysis has been remarkably scarce. Inspired by the - often misleading - 'carbene' label, which implies a substantial degree of M = C pi bonding, we have been interested in evaluating the potential of N-heterocyclic carbene complexes as building blocks for constructing electronically active materials. Electron mobility via the metal-carbon bond has been investigated in monometallic imidazol-2-ylidene complexes and subsequently expanded to polymetallic systems. In particular, ditopic benzobisimidazolium-derived ligands have been explored for the fabrication of bimetallic molecular switches and main-chain conjugated organometallic polymers. Electrochemical analyses have allowed the degree of electronic coupling between the metal sites to be quantified and the key parameters that govern the intermetallic communication to be identified.